When dental caries is deep enough to reach dental pulp, pulpectomy is usually performed for treatment of the caries. However, the dental pulp not only has a function to block external stimulus by reparative dentin formation, but also functions to inhibit further invasion of bacterial by sense and prevent tooth fracture caused by chewing a hard material with the sense of occlusion. In addition, the dental pulp can maintain protein and water in dentin by metabolism, and additionally keep the tensile strength and other properties of dentin. The dental pulp is also known to have an infection defense mechanism by immune system.
NiTi alloy rotary files are used popularly in endodontics, because of morphological complexity of the root canal. However, complete pulpectomy, enlargement of root canal and root canal filling are almost impossible. Thus, pulpectomy often leads to periapical periodontitis, and has high possibility of resultant loss of the tooth.
There is unmet need for development of a method to preserve the dental pulp as long as possible for longevity of teeth. Thus, technological development for a novel method for caries treatment is under progress to regenerate dentin and dental pulp by using triad of tooth regeneration: 1) morphogen (BMPs (bone morphogenetic proteins), etc.) 2) dental pulp stem cells, and 3) microenvironment (scaffold, extracellular matrix, etc.).
First, as described in Nonpatent Literature 1 and 2, there is, ex vivo cell therapy or gene therapy, to regenerate a large amount of dentin rapidly. In this method, BMP protein or BMP gene were introduced into dental pulp stem cells in vitro to induce their differentiation into odontoblasts in three-dimensional culture, and the differentiated odontoblasts were transplanted on the exposed pulp tissue.
As described in Nonpatent Literature 3, generation of a large number of human dental pulp stem cells, which does not cause transplant rejection, is now under progress for clinical application of the methods described above. And side population (SP) cells, which are highly enriched for stem cells, have been characterized by molecular biological methods.
When the dental pulp tissue is some kind of accidental exposure or reversible pulpitis, the dentin regeneration method described above would be effective. However when the tissue is irreversible pulpitis with pain, there is no choice but to perform pulpectomy.
In the case of autologous replantation in a human immature tooth with incomplete apical closure, it is known that the dental pulp is regenerated at high frequency after replantation. Additionally, the pulp regeneration is accompanied by mineralization in the pulp cavity and the root canal, root development and closure of apical dental foramen, thus preventing root fracture. Even if the dental pulp is necrotic, the remaining extracellular matrix may function, if there is no infection, as a scaffold for infiltration of blood vessels and cells.
The cells existing in the periapical tissue are still alive during replantation, and may migrate in the direction to the tooth crown and proliferate there in the root canal after replantation.
On the other hand, in the case of canine immature tooth, the dental pulp is regenerated similarly when the tooth is replanted even after complete removal of pulp tissue. There is a report on dental pulp regeneration even in the case of an immature tooth with periapical lesion. In this report, the root canal is cleaned, disinfected thoroughly, applied with three different kinds of mixture of antibacterial agents, and filled with blood clot to the cementodentinal junction. The cavity is further completely sealed with Mineral trioxide aggregate (MTA) and Cavit.
In addition, as described in Nonpatent Literature 4, it has been reported that, even in the case of canine healthy mature tooth, regeneration of dental pulp was observed, if the apical root is cut off to enlarge the apical foramen by apicoectomy followed by pulpectomy, and the tooth was replanted and filled with blood clot in the root canal.
However, most of the reports on pulp regeneration in the emptied root canal are those in immature teeth. In the case of deep caries with pulpitis or periapical periodontitis in mature teeth with complete apical closure, no method nor root canal filler for dental tissue regeneration have been developed yet.
Patent Documents 1 and 2 describe root canal fillers made of synthetic materials. However, in these cases, the root canal filler may be separated from the dentinal wall or ruptured after root canal filling. In addition, these root canal fillers may cause periapical periodontitis in several years.